1. Field of the Invention
This invention relates to a process for treating flue gases and, more specifically, to a process for purifying (conditioning) such flue gases by ammonia addition. More particularly, this invention relates to a process for flue gas treatment by ammonia addition, whereby the ammonia is derived from the hydrolysis of urea.
2. Description of Prior Art
It is well known to add ammonia to flue gases to remove, for instance, nitrogen oxides, which are formed in the course of combustion itself. Reaction between ammonia and nitrogen oxides, in the presence of oxygen, results in nitrogen and water formation in accordance with the following reaction: EQU 2NH.sub.3 +NO+O.sub.2 .fwdarw.3H.sub.2 O+N.sub.2
Ammonia gas is injected into the flue gas stream to be treated by vapor obtained by stripping of the ammonia contained in an ammonia aqueous solution in which the ammonia concentration is roughly 30% by weight. The ammonia aqueous solution has to be transported from the production plant to the user plant, stored, sent to a stripping plant to yield the desired ammonia, and then the ammonia containing residual water has to be neutralized before its disposal.
Ammonia solutions are presently classified as toxic materials. Consequently, certain specific rules have to be followed for its handling, due to the high volatility and pollution level of ammonia.
In order to avoid the aforementioned problems, use of non-toxic, harmless compounds has been proposed which, under the reaction conditions, may yield ammonia. For this purpose, urea has been used to generate ammonia without the formation of any undesired by-product. Use of urea as a conditioning agent of flue gases solves the problem connected with highly toxic material handling and storage; however, to obtain fine particles of solid urea and uniformly inject it into a flue gas stream still presents substantial problems.